1. Field of the Invention
The present invention relates to a plasma processing apparatus such as RIE (reactive ion etching) and CVD apparatuses and to a plasma cleaning method for use in the same.
2. Description of the Background Art
FIG. 11 is a cross-sectional view of a conventional RIE apparatus AP. There are provided first and second electrode conductors 3 and 4 in an internal space 2 of a conductive chamber 1. The first and second electrodes 3 and 4 are spaced apart from each other, and a clearance 5 is formed between the electrodes 3 and 4.
The first electrode 3 is supported by an insulator 6 mounted on an inner wall surface of the chamber 1 and is electrically insulated from the chamber 1 by the insulator 6. An extraction electrode 7 extending from the first electrode 3 is connected to a high-frequency power source 8 located outside the chamber 1.
The second electrode 4 is supported through a conductive pillar 9 by the inner wall of the chamber 1 and is electrically connected to the chamber 1 through the pillar 9. The second electrode 4 and pillar 9 are hollow in core, which forms a reactive gas introduction path 10. A multiplicity of small holes 4b are formed in a major surface 4a of the second electrode 4 which surface is opposite to the first electrode 3. The reactive gas introduction path 10 communicates with the internal space 2 of the chamber 1 by means of the small holes 4b.
A reactive gas conduit 11 is coupled to an outer wall of the chamber 1 in corresponding relation to the reactive gas introduction path 10. A reactive gas supply cylinder not shown is connected to the reactive gas conduit 11. When a reactive gas is introduced from the reactive gas supply cylinder to the reactive gas conduit 11, the reactive gas enters the internal space 2 of the chamber 1 by way of the reactive gas introduction path 10 and small holes 4b.
A predetermined position 12 on the outer wall of the chamber 1 is electrically connected to the high-frequency power source 8. The chamber 1 is formed with an outlet 13, which is connected to a vacuum exhaust mechanism (not shown) such as a vacuum pump.
In the RIE apparatus AP, the selective etching of a film to be etched which is formed on a major surface of a semiconductor wafer 20 is performed as follows. Initially, the semiconductor wafer 20 is placed on the first electrode 3, and the pressure in the internal space 2 of the chamber 1 is reduced by the vacuum exhaust mechanism.
The reactive gas is introduced from the reactive gas supply cylinder into the internal space 2 of the chamber 1 while a high-frequency current is fed between the electrodes 3 and 4 from the high-frequency power source 8. This allows a high-frequency electrical discharge to occur in the clearance 5 between the electrodes 3 and 4. The resultant high-frequency electric field causes the production of the plasma of the reactive gas, which etches the film formed on the semiconductor wafer 20. Reaction products generated by the etching are discharged through the outlet 13 to the outside of the chamber 1.
In the conventional RIE apparatus AP, however, some of the reaction products generated by the etching are not discharged smoothly but are diffused within the chamber 1 to stick to the electrodes 3, 4 and inner wall surface of the chamber 1. Such reaction products, when sticking to the electrodes 3, 4 and inner wall surface of the chamber 1 in large quantities, peel off and fall onto the semiconductor wafer 20 as a foreign matter, resulting in a defective plasma processing of the semiconductor wafer 20. For this reason, it is necessary to periodically clean the electrodes 3, 4 and inner wall surface of the chamber 1.
Recently, a plasma cleaning method has been proposed in which the reaction products inside the chamber 1 are eliminated by using the plasma in the plasma processing apparatuses such as RIE apparatuses.
In this method, another reactive gas is introduced into the internal space 2 of the chamber 1, and the plasma of the reactive gas is produced by the high-frequency electrical discharge similar to that in the etching processing. The plasma gasifies the reaction products which stick to the portions inside the chamber 1, and the gasified reaction products are eliminated by suction.
In the conventional RIE apparatus AP, however, since the produced plasma is designed to concentrate in the clearance 5 between the electrodes 3 and 4 for the purpose of efficient plasma etching, the plasma does not reach the inner wall surface of the chamber 1. The reaction products which stick to the inner wall surface of the chamber 1 cannot be sufficiently eliminated by the plasma cleaning. There has been a problem that the reaction products which stick to the portions inside the chamber 1 cannot be positively eliminated.